JPWO2006095416A1 - High frequency amplifier with attenuator - Google Patents

Abstract

In a high-frequency amplifier having an input terminal for receiving a reception signal from an antenna and amplifying the reception signal, a gate-grounded transistor having a gate grounded at a high frequency and an input terminal connected to a source, a drain of the transistor and a power source , An output terminal connected to a connection node between the drain and the load element, and an attenuator selectively inserted between the drain and the output terminal. An attenuator can be selectively inserted through a switch after the gate-grounded transistor. Therefore, since no attenuator or changeover switch is provided between the input terminal and the antenna, there is no thermal noise source, and deterioration of the noise figure can be suppressed. Also, by configuring the attenuator with a resistance element, it is possible to match the input impedance over a wide band.

Description

  The present invention relates to a high-frequency amplifier having an attenuator, and more particularly to a high-frequency low-noise amplifier having an attenuation function provided in a front-end circuit on the antenna side of a radio receiver.

  The front end of the wireless receiver is provided with a high frequency low noise amplifier for amplifying the received signal. This high-frequency low-noise amplifier is required to amplify the amplitude of a minute reception signal input from the reception antenna and to have a predetermined input impedance while suppressing an increase in noise. The reception antenna may receive a strong electric field input signal in addition to a minute reception signal. Therefore, it is necessary to provide an attenuator in the amplifier in order to attenuate such a strong electric field input signal.

  On the other hand, in recent years, it has been proposed that a front-end circuit is constituted by a CMOS circuit and is realized by a chip that is shared with a circuit for processing a baseband signal at a subsequent stage digitally. By configuring both the front-end circuit and the digital processing circuit as a CMOS circuit, it can be made into one chip, and the cost can be greatly reduced.

  1 and 2 are configuration diagrams of a conventional front-end circuit. In the example of FIG. 1, a variable attenuator 14 is provided between the antenna 10 and the high frequency low noise amplifier 16. A mixer 18 that multiplies the signal from the local oscillator 20 is provided at the subsequent stage of the low noise amplifier 16, and the high frequency input signal is converted into an intermediate frequency or baseband signal. The variable attenuator 14 is variably controlled with or without attenuation in response to a feedback control signal 22 from the subsequent stage. When a strong electric field input is received, the variable attenuator 14 attenuates so that the low noise amplifier 16 is not saturated. When the normal level input is received, the variable attenuator 14 does not perform the attenuation, and the received signal is directly input to the low noise amplifier 16. Such prior art is described in Patent Document 1.

In the example of FIG. 2, the low noise amplifier 16 and the attenuator 15 are provided in parallel, and the received signal is supplied to the mixer 18 via the low noise amplifier 16 by the switch SW, and the mixer 18 via the attenuator 15. Is switched to the case of supplying to. The switch SW is switched and controlled by a feedback control signal 24 from the subsequent stage. When a strong electric field input is received, it is switched to the attenuator 15 side, and the attenuator 15 attenuates. On the other hand, when a normal level input is received, switching to the low noise amplifier 16 side is performed, and the received signal is amplified by the low noise amplifier 16. Such prior art is described in Patent Document 2.3.
JP 2002-94408 A JP 2000-174650 A JP 2000-508497 A

In the circuit example of FIG. 1, since the variable attenuator 14 composed of an element serving as a thermal noise source is provided before the low noise amplifier 16, the noise figure NF deteriorates. The variable attenuator 14 is composed of, for example, a T-shaped resistor element circuit, and generates thermal noise of <v> ² = 4 kTR (T is temperature) for the resistance value R. When this variable attenuator 14 is provided, The thermal noise is added to the input signal of the low noise amplifier 16, which is not preferable. Even if the amplifier 16 has low noise, if thermal noise is added to the input signal, the overall noise figure (the ratio of the S / N ratio of the input signal to the S / N ratio of the output signal) deteriorates. Similarly, in the circuit example of FIG. 2, a changeover switch SW is provided in the preceding stage of the low noise amplifier 16. This change-over switch SW is formed of, for example, a MOS transistor, and the transistor is also a source of thermal noise. Therefore, the noise figure also deteriorates in the case of the circuit of FIG.

  Accordingly, an object of the present invention is to provide a high-frequency amplifier with an attenuator in which deterioration of noise figure is reduced.

  In order to achieve the above object, according to a first aspect of the present invention, in a high-frequency amplifier having an input terminal for receiving a reception signal from an antenna and amplifying the reception signal, the gate is grounded at a high frequency. , A grounded-gate transistor having the input terminal connected to the source, a load element provided between the drain of the transistor and a power supply, and an output terminal connected to a connection node between the drain and the load element And an attenuator selectively inserted between the drain and the output terminal.

  According to the first aspect described above, the attenuator can be selectively inserted through the switch after the common gate transistor. Therefore, since no attenuator or changeover switch is provided between the input terminal and the antenna, there is no thermal noise source, and deterioration of the noise figure can be suppressed.

  In the first aspect described above, according to a preferred embodiment, a first switch transistor is provided between the drain of the common-gate transistor and the output terminal, and a second switch transistor is provided between the drain and the attenuator. The switch transistor is provided with a third switch transistor between the attenuator and the output terminal, the first switch transistor is conductive, and the second and third switch transistors are non-conductive and the amplifier is not attenuated. Thus, an amplifier with attenuation is obtained when the first switch transistor is non-conductive and the second and third switch transistors are conductive.

  In the above preferred embodiment, the attenuator includes a first impedance element provided between the second and third switch transistors, and a second impedance element provided between the first impedance element and the power source. The second impedance element and the load element are connected in parallel.

  The attenuator may further include a third impedance element between the first impedance element and the output terminal.

  In the attenuator, the first, second, and third impedance elements may be any one of a resistance element and a capacitance element. In particular, in the case of a resistance element, since the high frequency characteristics are small, the input impedance can be adjusted to a desired value over a wide band.

  When a high frequency signal is handled, an inductor can be used instead of a resistor as the load element of the amplifier.

  Since the attenuator is inserted between the drain and the output terminal, it is not necessary to provide an attenuator or a switching element in front of the input terminal, there is no source of thermal noise, and noise factor degradation can be prevented. Further, since the grounded-gate amplifier uses a grounded-gate transistor, the input impedance can be adjusted in a wide band by adjusting the transconductance gm of the transistor (the ratio of the change in the drain current to the change in the gate voltage). Therefore, the low noise amplifier of the present invention can set the input impedance to a desired value in a wide band.

It is a block diagram of the conventional front end circuit. It is a block diagram of the conventional front end circuit. It is a principle diagram of the present invention. It is a circuit diagram of the high frequency low noise amplifier in a 1st embodiment. It is a circuit diagram of the high frequency low noise amplifier in 2nd Embodiment. It is a circuit diagram of the high frequency low noise amplifier in 3rd Embodiment. It is a circuit diagram of the high frequency low noise amplifier in 4th Embodiment. It is a figure which shows the simulation result of the amplifier with an attenuator in this Embodiment.

Explanation of symbols

Tr1: Common gate transistor IN: Input terminal OUT: Output terminal Tr2: Switch transistor Tr3, Tr4: Switch transistor ATT: Attenuator R1: Load element

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  FIG. 3 is a principle diagram of the present invention. The high frequency low noise amplifier 30 connected to the antenna 10 has an attenuator 32 therein, and no attenuator is provided between the input terminal IN and the antenna 10, and a switch element for inserting the attenuator is also provided. Not provided. The attenuator 32 inserts or does not insert an attenuation function into the amplifier 30 in response to the feedback control signal 34 from the subsequent stage. The output of the amplifier 30 is supplied to, for example, the mixer 18 where the frequency is converted.

  FIG. 4 is a circuit diagram of the high-frequency low-noise amplifier in the first embodiment. This high-frequency amplifier is composed of an amplifying circuit using a gate-grounded transistor Tr1 and an attenuator ATT. The gate of the amplifying transistor Tr1 is connected to the first bias voltage Bias1 via the resistor R2 and to the ground terminal GND via the capacitor C1, and is grounded at high frequency. If the bias circuit of the first bias voltage Bias1 is an ideal circuit, the impedance is sufficiently low in the signal frequency band. In that case, the gate of the transistor Tr1 is directly connected to the first bias voltage Bias1 to provide a resistor. There is no need for a circuit of R2 or capacitor C1. Also, in the frequency band where the signal is low, the impedance of the capacitor C1 looks high. In this case, it is better to eliminate the resistor R2 and the capacitor C1. The source SC of the transistor Tr1 is connected to the input terminal IN and is connected to the second bias voltage Bias2 through the inductor L1. Further, the drain DR of the transistor Tr1 is connected to the power supply VDD via a load element including the switch transistor Tr2 and the resistor R1. An output terminal OUT is provided at a connection point between the load element R1 and the drain DR. The switch transistor Tr2 is also a grounded gate transistor, and the amplifier has a configuration in which the grounded gate transistor is cascade-connected.

  Further, in this high frequency amplifier, an attenuator ATT is inserted between the drain DR and the output terminal OUT with the two switch transistors Tr3 and Tr4 interposed therebetween. The attenuator ATT includes a resistor R3 between the transistors Tr3 and Tr4 and a resistor R5 connected to the power supply VDD.

  In the above high-frequency amplifier, when the switch signal SWX is H level and SWZ is L level, the transistor Tr2 is turned on, the transistors Tr3 and Tr4 are turned off, and the attenuator ATT is disconnected. The grounded amplifying transistor Tr1 and the load element R1 operate as a grounded gate amplifier. As shown in the lower right of FIG. 4, the two bias voltages Bias1 and Bias2 have a relationship of Bias1> Bias2. The input signal INPUT is a signal that swings around the second bias voltage Bias2. When the input signal INPUT is input to the input terminal IN, the gate-source voltage of the amplifying transistor Tr1 changes, and the drain current Id changes following the change. The drain current Id flows through the resistor R1, which is a load element, and an output signal whose amplitude is amplified is generated at the output terminal OUT.

  The amplification factor is determined from the mutual conductance gm of the amplifying transistor Tr1 having a common gate and the load element R1. Further, by adjusting the mutual conductance gm, the input impedance can be adjusted to a desired value, for example, 50Ω in a wide band. That is, when viewed from the input terminal IN, the input impedance is a value determined by the transistor Tr1, the switch transistor Tr2, and the load element R1, and is determined mainly by the reciprocal (1 / gm) of the mutual impedance gm of the transistor Tr1. Therefore, the input impedance can be adjusted to a desired value by adjusting the mutual conductance gm of the transistor Tr1. This transconductance gm has less frequency characteristics compared to the case of grounded source, and can therefore match the input impedance over a wide band. Therefore, the gate-grounded amplifying transistor itself can be amplified in a wide band.

  Next, in the high frequency amplifier, when the switch signal SWX is L level and SWZ is H level, the transistor Tr2 is non-conductive, the transistors Tr3 and Tr4 are conductive, and the attenuator ATT is connected. That is, an attenuator ATT composed of resistors R3 and R5 is inserted between the drain DR of the amplifying transistor Tr1 and the output terminal OUT. Although the drain current Id changes according to the input signal INPUT, the drain current Id flows to the resistors R5 and R3 of the attenuator ATT in addition to the resistor R1 that is a load element. As a result, the signal amplitude at the output terminal OUT is suppressed and attenuated, and the saturation of the amplifier is suppressed even when a strong electric field is input.

  Further, the attenuator ATT has a resistor R5 connected to the power supply VDD in parallel with the load element R1. Thereby, an increase in input impedance due to insertion of the attenuator ATT is reduced, and the input impedance is maintained at a desired value (for example, 50Ω). That is, since the input impedance is determined by the transistor Tr1, the resistor R3, the parallel resistors R5 and R1 when viewed from the input terminal IN, the attenuating operation in which the attenuator ATT is inserted by providing the resistor R5 in parallel with the load resistor R1. It is possible to suppress an increase in input impedance over time.

  And since the attenuator ATT is comprised by resistance element R3, R5, it is hard to receive to the influence of a frequency characteristic. That is, in the case of a resistance element, since the frequency component is not included in the impedance, input impedance matching can be performed over a wide band even during an attenuation operation, and signal deterioration due to signal reflection at the input terminal can be prevented.

  FIG. 5 is a circuit diagram of a high-frequency low-noise amplifier according to the second embodiment. In this example, the difference from the circuit of FIG. 4 is that the attenuator ATT has R4 in addition to the resistors R3 and R5. The other configuration is the same as that of the amplifier of FIG.

  In the amplifier of FIG. 5, the amplification operation in which the transistor Tr2 is turned on and the transistors Tr3 and Tr4 are turned off is the same as the amplifier of FIG. Further, the following operation is performed when the transistor Tr2 is turned off and the transistors Tr3 and Tr4 are turned on. First, the drain DR signal is attenuated by resistance division by the resistors R3 and R5, and the attenuated signal is generated at the node N1. The attenuated signal at the node N1 is further attenuated by the resistors R4 and R1, and an attenuated signal is generated at the output terminal OUT. Therefore, by inserting the resistor R4, the attenuation rate can be further increased as compared with the operation at the time of attenuation shown in FIG.

  The high-frequency low-noise amplifier of FIG. 5 can perform a wide-band amplification operation as in the case of FIG. 4, and can also perform input impedance matching over a wide band during the attenuation operation. Since no thermal noise source such as an attenuator or a changeover switch is provided between the amplifier consisting of the transistors Tr1, Tr2 and the resistor R1 and the input terminal IN, it is possible to prevent the noise figure from deteriorating.

  FIG. 6 is a circuit diagram of a high-frequency low-noise amplifier according to the third embodiment. In this example, the difference from the circuit of FIG. 5 is that the ground GND is connected to the resistor R5 of the attenuator. Other configurations are the same as those in FIG. In such a circuit configuration, the resistor R5 is connected to the ground GND instead of the power supply VDD. However, since both the power supply and the ground are large-capacity power supplies, the resistor R1 + R4 and the resistor R5 are connected in parallel for small signals. Is equivalent to Therefore, the input impedance can be reduced by the resistor R5. Further, the signal at the output terminal OUT is attenuated by the resistor R4. Furthermore, the attenuation rate can be further increased by providing the resistor R3. Even if the resistor R3 is omitted, a certain amount of attenuation can be performed by the resistor R4.

  FIG. 7 is a circuit diagram of a high-frequency low-noise amplifier according to the fourth embodiment. In this circuit, the attenuator ATT includes capacitors C1, C2, and C3, and the capacitor C2 is connected to the ground GND. The capacitor C2 may be connected to the power supply VDD as in the first and second embodiments. Since both the ground GND and the power source VDD are large-capacity power sources, both are equivalent to the ground power source in terms of AC. The other configuration is the same as that of the amplifier of FIGS.

  4 and 5, the amplifier operates as a gate-grounded amplifier composed of transistors Tr1 and Tr2 and a load element R1 in the same manner as in FIGS. The input impedance can be adjusted over a wide band by adjusting the inductance. On the other hand, during the attenuating operation, an attenuator ATT composed of three capacitors is inserted between the drain DR and the output terminal OUT. In this case, the signal at the drain DR is attenuated by the impedance division by the capacitors C1 and C2, and is generated at the node N1, and the signal at the node N1 is further attenuated by the impedance division by the resistor R1 and the capacitor C3, and an attenuation signal is output to the output terminal OUT. Is done.

  In the case of the fourth embodiment, since the attenuator ATT is composed of three capacitors, their impedance has frequency characteristics. Therefore, it is inferior to the examples in FIGS.

  FIG. 8 is a diagram showing a simulation result of the amplifier with an attenuator in the present embodiment. This embodiment is the high frequency low noise amplifier circuit shown in FIG. FIG. 8A shows the input power versus output power characteristic (Pin-Pout characteristic) during the amplification operation, and FIG. 8B shows the input power versus output power characteristic (Pin-Pout characteristic) during the attenuation operation. The horizontal axis represents the input power Pin and the vertical axis represents the output voltage Pout, which shows the difference between the input power versus output power characteristic (Pin-Pout characteristic) and the ideal linear characteristic of the power characteristic.

  At the time of amplification operation, as shown by the difference 54 between the input / output power characteristic 52 and the ideal linear characteristic 50, the input power at which the difference 54 becomes 1 dB, and the input P1dB is about −25 dBm. If the input is less than or equal to P1 dB, the input / output power characteristic 52 has a substantially linear characteristic. Further, during the attenuating operation, as indicated by the difference 64 between the input / output power characteristic 62 and the ideal linear characteristic 60, the input P1dB has an input power Pin of about −5 dBm. Obviously, the linear characteristic can be maintained with respect to the input of higher power than in the amplification operation.

  As described above, according to the present embodiment, since the attenuator and switch means serving as a thermal noise source are not provided in the previous stage of the amplifier circuit, the noise figure is not deteriorated. In addition, the input impedance can be matched with a wide frequency during the attenuation operation.

  The present invention is a high-frequency low-noise amplifier that receives a wide-band input signal.

Claims (6)

In a high-frequency amplifier having an input terminal for receiving a reception signal from an antenna and amplifying the reception signal,
A gate-grounded transistor having a gate grounded at a high frequency and a source connected to the input terminal;
A load element provided between the drain of the transistor and the power source;
An output terminal connected to a connection node between the drain and the load element;
And a high-frequency amplifier having an attenuator selectively inserted between the drain and the output terminal.   2. The first switch transistor according to claim 1, wherein a first switch transistor is provided between the drain and the output terminal of the common-gate transistor, and a second switch transistor is provided between the drain and the attenuator. A third switch transistor is provided between the first switch transistor and the first switch transistor; the first switch transistor is conductive; the second and third switch transistors are non-conductive; A high frequency amplifier which becomes an amplifier with attenuation when the transistor is non-conductive and the second and third switch transistors are conductive.   The attenuator according to claim 2, wherein the attenuator includes a first impedance element provided between the second and third switch transistors, and a second impedance element provided between the first impedance element and a power source. A high frequency amplifier having a second impedance element and the load element connected in parallel.   4. The high-frequency amplifier according to claim 3, wherein the attenuator further includes a third impedance element between the first impedance element and an output terminal.   5. The high-frequency amplifier according to claim 4, wherein the first, second, and third impedance elements are either resistance elements or capacitance elements. 2. The gate of the grounded-gate transistor according to claim 1, wherein the gate is connected to the ground via a capacitive element, is connected to a first bias voltage via a resistive element, and the source is connected to a second bias via an inductor. High frequency amplifier connected to voltage.

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